The letter was referenced in a Thursday filing by UniFirst to the Securities and Exchange Commission. In the filing, UniFirst wrote that the demand relates to the once-a-month cleaning services they provided to NECC’s cleanroom facilities.

UniFirst spokesman Adam Soreff said in a statement the company’s UniClean business sent two technicians to NECC monthly for 90 minutes each. He said the cleaners used the NECC’s own cleaning solution.

“UniClean was not in any way responsible for NECC’s day-to-day operations, its overall facility cleanliness, or the integrity of the products they produced,” he said.

A tainted steroid produced by Framingham-based NECC, and given mainly for back pain, has been tied to the fungal meningitis outbreak, which was discovered in Tennessee in September. The company has shut down and recalled its products. Inspections at NECC’s facility found various potential contaminants, including standing water and mold. Last month, the company declared Chapter 11 bankruptcy and said it was seeking to set up a fund to pay victims.

Messages were left for the attorney for NECC’s insurance company requesting comment, including on whether letters similar to the one sent to UniFirst have or will be sent to other companies.